1. Field of the Invention
The present invention relates to an image reading device that uses an erecting equal-magnification lens array formed of a plurality of lens array plates.
2. Description of the Related Art
Some image reading devices such as scanners are known to use erecting equal-magnification optics. Erecting equal-magnification optics are capable of reducing the size of devices better than reduction optics. In the case of image reading devices, an erecting equal-magnification optical system comprises a line light source, an erecting equal-magnification lens array, and a line image sensor.
A rod lens array capable of forming an erect equal-magnification image is conventionally used as an erecting equal-magnification lens array in an erecting equal-magnification optical system. Recently, there is proposed a lens array unit formed as a stack of a plurality of transparent lens array plates built such that the optical axes of individual convex lenses are aligned, where each transparent lens array plate includes a systematic arrangement of micro-convex lenses on both planes (see, for example, patent document No. 1). Since a lens array unit such as this comprises a stack of lens array plates formed by, for example, injection molding, an erecting equal-magnification lens arrays can be manufactured at a relatively low cost.
A lens array unit lacks a wall for beam separation between adjacent lenses. Therefore, there is a problem of stray light wherein a light beam diagonally incident on a lens array unit travels diagonally inside the plate and enters an adjacent convex lens, creating a ghost image as it leaves the plate.
Patent document No. 1 discloses a technology to address stray light whereby a light shielding member for shielding unwanted light traveling from an object to be imaged is fitted to the first lens array facing the object. Further, patent document No. 2, for example, discloses a technology whereby a light shielding mask is fitted to the first lens array facing an object to be imaged and to the second lens array facing the photosensitive device.    [patent document No. 1] JP 2001-352429    [patent document No. 2] JP 2003-302504
In the case of the lens array unit described in patent document No. 1 or patent document No. 2, the number of components is increased as a result of providing a light shielding member or a light shielding mask, with the result that the cost of an image reading device having the lens array unit built in may be increased.